A transgenic approach to identify thyroxine transporter-expressing structures in brain development.

Area of Science:

• Neuroscience
• Endocrinology
• Developmental Biology

Background:

• Thyroid hormone metabolism is crucial for brain development.
• Thyroxine (T4) transport into the adult brain occurs via SLCO1C1 (OATP14) at the blood-brain barrier and choroid plexus.
• T4 transport mechanisms in the developing brain, particularly before blood-brain barrier maturation, are poorly understood.

Purpose of the Study:

• To investigate the expression pattern of SLCO1C1 during brain development.
• To determine if SLCO1C1 is expressed in neuronal progenitor cells or developing neurons.
• To explore the functional significance of SLCO1C1 expression in neuronal development and thyroid hormone sensitivity.

Main Methods:

• Generation of Slco1c1-Cre transgenic mice using bacterial artificial chromosome recombineering.
• Crossing Slco1c1-Cre mice with Rosa26 reporter mice to visualize Cre activity.
• Histological analysis (β-galactosidase staining) to map Cre expression.
• Assessment of neuronal progenitor markers (TBR2) and effects of maternal hypothyroxinaemia.

Main Results:

• Cre expression, driven by the Slco1c1 locus, was detected in neurons of the developing brain, including cortical layer 2/3 and hippocampus.
• SLCO1C1 expression was observed in neuronal progenitors (TBR2-positive cells) at embryonic day 15.
• Maternal hypothyroxinaemia led to a reduction in β-galactosidase-positive neurons in the developing cortex, indicating T4 sensitivity.

Conclusions:

• SLCO1C1 is expressed in the neuronal cell lineage during critical periods of brain development.
• This developmental expression suggests a role for SLCO1C1 in mediating thyroid hormone effects on specific neuronal populations.
• SLCO1C1 expression may explain the heightened sensitivity of certain developing neurons to thyroid hormone deficiency.